1. Field of the Invention
The present invention relates to a phase comparison protective relay for a transmission line for detecting an internal fault.
2. Description of the Prior Art
The purpose of a phase comparison protective relay is to detect an internal fault by comparing the phases of current at the terminals of the transmission line. When current is received at both terminals from the internal fault, the internal fault can be easily detected. However, difficulties have been encountered in the so called single source system where current is received at only one terminal from the internal fault. Although these difficulties are relatively easy to deal with where the power source terminal in the conventional single source system is fixed, in a long distance transmission line, the fault currents at both terminals are quite different depending upon where the internal fault point is found in the 500 KV system making it necessary to use variable power sources at both terminals.